This disclosure relates to a silicate phosphor and a white light emitting device that uses the silicate phosphor.
A conventional optical system may include fluorescent lamps and incandescent lamps. Fluorescent lamps, however, cause environmental problems due to mercury (Hg) contained therein. In addition, such conventional optical systems have very short lifetimes and because they operate at a low efficiency, they do not save much energy. Therefore, much research is being performed to develop white light emitting devices that operate at a high efficiency.
Such white light emitting devices can produce white light using three methods as follows. Red, green and blue phosphors can be excited by a UV light emitting diode (LED) that acts as a light source to produce white light, red and green phosphors can be excited by a blue LED that acts as a light source to produce white light, or a yellow phosphor can be excited by a blue LED that acts as a light source to produce white light.
Specifically, the method of producing white light by exciting a yellow phosphor by a blue LED is problematic in terms of color production because the intensity of red light contained in the white light is decreased.
Therefore, research into optical systems that use the other two methods, that is, the method that uses the UV LED and red, green and blue phosphors and the method that uses the blue LED and red and green phosphors, is being actively performed. These methods can produce excellent color properties but only at a low efficiency.
Commercially available red phosphors are not very suitable for a white light emitting device. They show excellent emission efficiency with respect to cathode rays, vacuum ultraviolet rays (VUV) and short waves, but low emission efficiency with respect to UV and blue light used in white light emitting devices. Therefore, there is a need to develop a red phosphor having high emission efficiency with respect to UV and blue light in the technical field of white light emitting devices.
In view of the above, a silicate-based phosphor has been developed. For example, Chem. Mater., Vol. 18, 5267 (2006), IEICE Trans. Electron. Vol. E89-C, 1406 (2006) discloses a white light emitting device including Li2SrSiO4:Eu as an orange-yellow phosphor which is excited by a blue LED light source to produce white light.